The invention relates to an apparatus for stiffening and/or correcting a part of the vertebral column consisting of at least two vertebrae, according to the precharacterizing clause in claim 1.
Apparatuses of this kind for stiffening and/or correcting a part of the vertebral column consisting of at least two vertebrae are known in the state of the art. Such an apparatus comprises at least two screw-like retaining devices, which can be appropriately fixed to one of the vertebrae in the affected part of the vertebral column. The retaining devices are provided to receive and hold in place a compression or distraction rod that connects the retaining devices to one another. This arrangement allows stiffening or so-called spondylodesis of individual parts of the vertebral column and/or correction in cases of spinal curvature (scoliosis, kyphosis), misalignment (rotation), injury (trauma), neoplasms (tumor) and in particular abrasion or degenerative spinal disease, according to the principle of osteosynthesis that is as rigid as possible and hence extremely stable mechanically.
The retaining devices in these apparatuses as a rule take the form of screws or so-called pedicle screws as well as hooks known per se, which can be connected to one another by way of a mechanically stable compression or distraction rod. An aspect of these apparatuses that has proved decidedly disadvantageous is the structure of the part that connects each retaining device to the compression or distraction rod. On the one hand, the height of the connecting part of these apparatuses is usually relatively great, which severely delays healing after surgery. On the other hand, various mechanical problems are encountered in assembling the apparatus, which both prevent permanent fixation and make it impossible to carry out corrective repositioning later on. Another disadvantage of these apparatuses is that they offer little or no opportunity to vary the length of the fixed region. Instead, different apparatuses must be used, some exclusively for short lengths and others exclusively for great lengths, and because they are not interchangeable their versatility in use is severely restricted. Furthermore, only a very limited force can be applied to these apparatuses, not least because of their construction, in order to correct misalignments of the affected part of the spine. Finally, all these apparatuses are also relatively expensive.